Cosmetic products are produced by using various emulsion systems (emulsion compositions) such as oil in water (O/W) emulsion, water in oil (W/O) emulsion, and water-in-silicone oil (W/S) emulsion to convey various components.
Cosmetic composition for skin care is directly applied to the skin, and therefore, the demands for such composition include not only the functionality but also good skin feeling. Recently, there is a growing interest for a sensuous cosmetic product which is capable of providing unique feeling during or after the use of the composition by the change of the emulsion system (emulsion composition) or the composition of the system.
An example is cool feel cosmetic composition having a menthol derivative added in the cosmetic composition (for example, Patent Document 1: Korean Patent No. 10-1084875). Another example is a cosmetic composition comprising a cationic copolymer containing monomer unit selected from acryloylethyltri(C1-C3 alkyl) ammonium salts and a mica having a carbon dioxide coating, and this cosmetic composition realizes a smooth skin by soft focus effect. (See for example, Patent Document 2: WO 2009/103602.)
Another type of products that are in focus is waterdrop quick break type products which intensively supply water component to the skin simultaneously with the application of the product to the skin by bursting of the waterdroplets.
Also disclosed is a cosmetic product providing the skin with a moist feeling like that of the lotion as well as cool feeling and humectant feeling, and which has also realized excellent make up effects and stability. This composition is prepared by mixing PEG/PPG-19/19 dimethicone or lauryl PEG-9 polydimethylsiloxyethyl dimethicone with the oil phase of the water-in-oil emulsion composition, and when applied to the skin, the interior aqueous phase is instantaneously released simultaneously with the breakage of the emulsion of the water-in-oil foundation emulsion. (See for example, Patent Document 3: Korean Patent No. 10-1158281.)
Water-in-silicone and silicone-in-water emulsion compositions having excellent waterdrop quick break effect, cosmetic retention, skin adhesion, and skin feeling are also proposed. The emulsion composition comprises a polyionic complex of an anionic hydrophilic macromolecule substance bonded with a hydrophobic cationic monomer by ionic bond, a silicone based crosspolymer, and a silicone oil. (See for example, Patent Document 4: Korean Patent No. 10-1070819.)
As disclosed in the Patent Document 3, the emulsion composition should be highly stable at various temperatures if the emulsion composition is to be used in a cosmetic product.
Stability of the cosmetic composition is generally evaluated in a cyclic evaluation by observing the dispersion state of the emulsion at different temperatures (high temperature, low temperature, and room temperature) and in different atmospheres. Patent Document 3 discloses an observation of the dispersion state by repeating the incremental 1 month cycle of 45° C.→room temperature→5° C. In this case, the observation is conducted by occasionally changing the temperature and time depending on the dosage form of the cosmetic product.
The use of 5° C. for the “low” temperature may be adequate in the case of the indoor use. The cosmetic product, however, may be exposed to a lower temperature in the delivery and storage of the cosmetic product, and also, in the use of the product in colder district, and at a temperature lower than 5° C., there is a risk that the emulsion is destroyed inviting separation of the aqueous phase part and the oil phase part.
Accordingly, the product is also tested by a freeze test at a temperature of lower than −20° C., and also, by a repeated freeze-thaw stability test cycles as a preparation for shipping to cold district.